This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We continue to develop the utility of mass spectrometry to assist in the definition of integral membrane proteins and (especially ion channels) at atomic resolutions using diffraction methods. A number of publications have resulted from this work D.A. Doyle, J.M. Cabral, R.A. Pfuetzner, A. Kuo, J.M. Gulbis, S.L. Cohen, B.T. Chait, R. MacKinnon, "The Structure of the Potassium Channel: Molecular Basis of K+ Conduction and Selectivity" Science 280, (1998) 69-77. R. MacKinnon, S.L. Cohen, A. Kuo, A. Lee, B.T. Chait "Structural Conservation in Prokaryotic and Eukaryotic Potassium Channels" Science 280 (1998) 106-109. J.H. Morais Cabral, A. Lee, S. Cohen, B.T. Chait, M. Li, R. MacKinnon "Structure of the HERG potassium channel amino-terminal domain: definition of a structural family of PAS domains" Cell 95 (1998) 649-655. J.M. Gulbis, M. Zhou, S. Mann, R. MacKinnon "Structure of the Cytoplasmic ( Subunit-T1 Assembly of Voltage-Dependent K+ Channels" Science 289(2000) 123-127. M. Cadene, B.T. Chait "A Robust Detergent-Friendly for Mass Spectrometric Analysis of Integral Membrane Proteins" Anal. Chem. 72 (2000) 5655-5658. S.L. Cohen, B.T. Chait "Mass Spectrometry as a tool for Studying Protein Structure" Ann. Reviews of Biophysics and Biomolecular Structure 30 (2001) 67-85. R. Dutzler, ER Campbell, M. Cadene, B.T. Chait, R.MacKinnon "X-ray structure of a ClC chloride channel at 3.0 A reveals the molecular basis of anion selectivity" Nature 415 (2002) 287-94. Y. Jiang, A. Lee, J. Chen, M. Cadene, B. T. Chait, R. MacKinnon "Crystal structure and mechanism of a calcium-gated potassium channel" Nature 417 (2002) 515-522. Y. Jiang, A. Lee, J. Chen, M. Cadene, B. T. Chait, R. MacKinnon "The open pore conformation of potassium channels" Nature 417 (2002) 523-526. Y. Jiang, A. Lee, J. Chen, V. Ruta, M. Cadene, B.T. Chait &Roderick MacKinnon "X-ray structure of a voltage-dependent K+ channel" Nature 423 (2003) 33-41;280. M. Nishida1, M. Cadene, B.T. Chait, R. MacKinnon "Crystal structure of a Kir3.1-prokaryotic Kir channel chimera" EMBO Journal, 26 (2007) 4005-4015